Process of dehalogenation and dehalogenation with simultaneous reduction of 11a-halo-6-deoxy-6-demethyl-6-methylenetetracyclines by hydrazine

ABSTRACT

1. A PROCESS OF DEHALOGENATION AND SIMULTANEOUS DEHALOGENATION AND REDUCTION OF C6- OF A 11A-CHLORO-6-DEOXY-6-DEMETHYL-6-METHYLENETETRACYLINE, WHEREIN THE 11ACHLORO DERICATIVE IS DEHALOGENATED AT C11A- BY EQUIMOLECULAR AMOUNTS OF HYDRAZINE TO YIELD THE RESPECTIVE 6-DEOXY6-DEMETHYL-6-METHYLENETETRACYCLINES, AND SIMULTANEOUSLY DEHALOGENATED AT 11A- AND REDUCED AT C6- BY AT LEAST TWO EQUIMOLECULAR AMOUNTS OF HYDRAZINE TO YIELD THE RESPECTIVE 6-DEOXYTETRACYCLINES, IN THE PRESENCE OF CATALYTIC AMOUNTS OF A NOBLE METAL CATALYST SELECTED FROM THE GROUP CONSISTING OF PALLADIUM, PLATINUM, AND RHODIUM IN AN INERT REACTION MEDIUM, AND THE COMPOUNDS THUS FORMED ARE RECOVERED SUBSEQUENTLY FROM THE REACTION MIXTURE.

Uti'itec'l States Patent m 3,849,491 PROCESS OF DEHALOGENATION AND DEHALO- GENATION WITH SIMULTANEOUS REDUCTION OF 11a HALO 6 DEOXY 6 DEMETHYL-6- METHYLENETETRACYCLINES BY HYDRAZINE Ivan Villax, 1 Trevessa do Ferreiro, Lisbon 3, Portugal No Drawing. Filed July 2, 1971, Ser. No. 159,458 Claims priority, application Portugal, July 3, 1970,

54,106, 54,107, 54,108 Int. Cl. C07c 103/19 US. Cl. 260559 AT Claims ABSTRACT OF THE DISCLOSURE A process of dehalogenation and dehalogenation with simultaneous reduction of lla-halo-6-deoxy-6-demethyl-6- methylenetetracyclines by hydrazine is provided.

The 6-deoxy-6-demethyl6-rnethylenetetracyclines and 6-deoxytetracyclines are valuable antibiotics, of which the most important are 6-deoxy-6-dimethyl-6-methylene-5-hydroxy-tetracycline (methacycline) and a-6-deoxy-5-hydroxytetracycline (deoxycycline).

Various processes have been described for the preparation of the 6-deoxy-6-dimethyl-6-methylenetetracyclines. The first of such disclosures is in Portuguese Pat. No. 36,099 by the same inventor of the present application. German Pat. No. 1,156,405 and British Pat. No. 951,663, as well as US. Pat. No. 2,984,686, also describe various routes for preparing the 6-deoxy-6-dimethyl-6-methylenetetracyclines.

The 6-deoxytetracyclines are obtained through catalytic hydrogenation of tetracycline, oxytetracycline and chlorotetracycline, yielding the 3-6-isomers (U.S. Pat. No. 3,019,- 260), or through catalytic hydrogenation of methacycline or lla-halo-methacycline, yielding a mixture of the aand fi-isomers in a variable proportion (US. Pat. No. 3,200,149). The a-isomers, without the concomitant [3- isomer, are obtained according to U.S. Pat. Nos. 3,165,531 and 3,484,483, and Portuguese Pat. No. 52,217.

The present invention provides a new process to obtain in a nearly stoichiometric yield the 6-methylenetetracyclines and in a satisfactory yield the 6-deoxytetracyclines, by avoiding the inconveniences of the previous processes.

The starting material used to perform the present invention is the 1la-chloro-6-deoxy-6-clemethyl-6-methylenetetracyclines, which were first described in Portuguese Pat. No. 36,099 of May 19, 1959.

It has been found that the 1la-chloro-6-deoxy-6-demethyl-6-methylenetetracyclines are easily dehalogenated, without destruction of the molecules, by hydrazine when used in an equimolar amount in the presence of a catalytic amount of palladium charcoal in a inert reaction medium, to yield the 6-methylenetetracyclines and 6-deoxytetracyclines, by the same process, when the amount of hydrazine present is, at least, two equivalents and the catalyst is preferably platinum.

A considerable advantage of the present process lies in the fact that the secondary product of the reaction is nitrogen, which naturally does not interfere with isolation of the final product in pure state.

The process described in German Pat. No. 1,156,405 and in British Pat. No. 951,663 obtains the 6-deoxy-6-demethyl-6-methylenetetracyclines by acid dehydration of the 12-sulphuric acid ester of tetracycline, but yields are rela tively low due to a partial decomposition of the methylenetetracyclines in the strongly acid media. Portuguese Pat. No. 36,099 describes the use of dehalogenation of the 11ahalo-6-deoxy-6-demethyl-6-methylenetetracyclines by hy- 3,849,491 Patented Nov. 19, 1974 drosulfite, and in US. Pat. No. 2,984,686, the Ila-dehalogenation is carried out by zinc and a mineral acid, iron and diluted hydrochloric acid, alkali metal hydrosulfite in aqueous media, sodium iodide in a halogen acceptor medium, such as acetone, and by catalytic hydrogenation. In all the above processes, with the exception of catalytic hydrogenation, by-products, such as zinc chloride, iron chloride, free sulphur (often in collodial state), sodium iodide and chloride are formed, which have to be separated from the methylenetetracyclines thus prepared. However, this is a difficult procedure and diminishes considerably the final yield. The catalytic hydrogenation does not yield secondary products per se, but it provokes destruction, to a considerable extent, of the molecules to be dehalogenated, as well as a concomitant formation of uand B- deoxytetracyclines, according to my experience, even if the hydrogenation were stopped when exactly an equimolar amount of hydrogen, necessary for dehalogenation, has been taken up.

The hydrazine-palladium charcoal dehalogenation is more advantageous than the direct catalytic hydrogenation insofar as it does not require pressure or a special apparatus. It is less hazardous than catalytic hydrogenation, causes no destruction of the molecules to be dehalogenated, and finally the concomitant formation of uand fi-6-deoxytetracyclines is negligible if none or only a slight excess over the equimolecular amount of hydrazine is used, the catalyst being preferably palladium on charcoal.

When using at least two equivalents of hydrazine or an excess of same, and especially if the catalyst is platinum, the dehalogenation is accompanied by simultaneous reduction of the 6-methylene bond, yielding the 6-deoxytetracyclines. It is surprising that the reaction in this process takes place at Cllaand C6- simultaneously, and not stepwise, first at Cllaand subsequently at C6-, as it would have been expected. In view of the fact that preparation of the ocand e-isomers is dependent on the pH, a slightly acid pH range, near to neutral, favors the formation of the a-isomer, but it also favors the formation of degradation products. At pH 3, the proportion of the aand B-isomers is around 1:1, whereas under more acid conditions the formation of the ,B-isomer increases. A few experiments will establish the optimum pH range for each starting material, and which in practice can easily be maintained at a constant rate by the continuous addition of hydrazine solution, thus neutralizing the hydrohalic acid formed during dehalogenation. In comparison to catalytic hydrogenation, it is to note that the formation of degradation products is much less pronounced at a given pH when using hydrazine as dehalogenating and reducing agent.

When preparing the 6-deoxytetracyclines, a certain amount of 6-deoxy-6-dimethyl-G-methylenetetracyclines will also be formed in the reaction mixture, and in view of the fact that these latter are also valuable commercialized antibiotics, they may be isolated together with the 6- deoxytetracyclines and subsequently separated. My copending Portuguese application No. 54,109 which corresponds to US. application 159,462, filed on July 2, 1971, provides a process for performing such isolation and separation.

The starting material used in the present invention is the 11a-chloro-6-deoxy-6-demethyl 6 methylcnetetracyclines, under the form of free base, an acid addition salt, such as hydrochloride, hydrofluoride, p-toluene-sulfonate.

The suitable reaction medium for performing the hydrazine reduction is a lower aliphatic alcohol, tetrahydrofuran, dioxane, lower dialkylformamide, acetone, water, or mixtures thereof. When 11a-chloro-6-deoxy-6-demethyl-6-methylene-5-hydroxytetracycline is the starting material and the initial pH is higher than 3, it is preferred to use anhydrous media to perform the reaction. For carry- 3 ing out this process, one can use hydrazine hydrate or a hydrazine acid addition salt, such as hydrochloride or sulphate.

The reaction temperature is not critical, being comprised between 10 to +50 C. However, when preparing the 6-deoxytetracyclines, a higher temperature range, between 25 to 50 C. is preferred.

The noble metal catalyst preferred is palladium, when preparing the 6 methylenetetracyclines, and platinum, when preparing the 6-deoxytetracyclines; however, rhodium may also be used. The amount of catalyst used for preparing the 6-methylenetetracyclines is not critical; as little as 0.001 part of 5% palladium charcoal per part of lla-halo-tetracycline will readily promote the dehalogenation, although the reaction is slow. For preparing the 6- deoxytetracyclines, approximately 0.1 part of platinum on a suitable support, such as carbon, is necessary. These amounts may be increased up to 2 parts, without provoking a further destruction of the molecules.

The isolation of 6-methylenetetracyclines can easily be performed by conventional methods, such as by filtering the reaction mixture and acidifying it with ethanolic or methanolic hydrogen chloride, thus yielding the hydrochloride in pure state. Likewise, any other acid addition salt of the 6-methylenetetracyclines can be obtained by treating the filtered reaction mixture with the desired acid and provoking crystallization by addition of a non-solvent. A process for the isolation and purification of 6-deoxytetracyclines is described in my co-pending Portuguese No. 54,109.

With a view to facilitating the performance of the present invention, the preparation of the starting mate rials therein used, according to the process described in Portuguese Pat. No. 36,099 (1959), is described in the examples appearing hereafter, by way of illustration, thereby introducing further improvements and practical details.

Preparation of 11achloro5-hydroxytetracycline, according to Portuguese patent application No. 36,099

with water and acetone and then dried at 10 C., yielding I the 11a-chloro-5-hydroxytetracycline in the form of 6,12- ketal. Melting point 177178 C. with decomposition, [aJ 27.5 (c.=1 in methanol containing 1% concentrated aqueous hydrochloric acid),

* i 'fm. 430 at 266 III/15:2

in methanol containing 1% concentrated hydrochloric acid. The infrared curve shows no absorption maximum in the 5 region at 5 .9/.L.

(b) 13.5 grs. of N-chlorosuccinimide is added quickly to a solution containing 46.5 grs. of anhydrous oxytetracycline base in 200 mls. of diethoxyethane and 0.5 mls. of triethylamine at 0 C., under strong stirring. At the end of 6 minutes, 1000 mls. of water is added (the pH adjusts automatically to around the isoelectric point), thus yielding an off-white precipitate. It is filtered and washed with water, yielding 11.6 grs. of l1a-chloro-S-hydroxytetracycline as 6,12-hemiketal.

(c) grs. of oxytetracycline hydrochloride in 225 mls. of dimethylformamide and 7.1 mls. of triethylamine in 25 mls. of dimethylformamide are added together, and the mixture is cooled to 10 C., under strong stirring. 7 grs. of N-chlorosuccinimide is added quickly, and at the end of 2 /2 minutes 750 mls. of a mixture of water and ice is then added. At the end of 12 minutes, the thick p p tate thus formed is diluted by addition of 375 mls. of a mixture of water and ice. It is filtered, and washed with water and acetone, yielding, when dried, the 11a-chloro-5-hydroxytetracycline-6,12-hemiketal. Melting point: 180185 C. with decomposition, [a1 25:2.5 (c.=1% in methanol containing 1% concentrated hydrochloric acid),

1312", 432 at 266 rm; and 91 at 340-345 111 in methanol containing 1% concentrated hydrochloric acid.

(d) 5 grs. of 11a-chloro-5-hydroxytetracyc1ine as the 6,12-hemiketal base, obtained according to (a), (b) or (c), is mixed with 4 mls. of methanol and 30 mls. of isopropyl alcohol. 26 mls. of absolute ethanol containing 17% weight/weight of anhydrous hydrogen chloride is then added. The product dissolves, after which it begins to crystallize. At the end of 18 hours at room temperature, the precipitate is filtered and washed with isopropyl alcohol. The non-reacted portion of the lla-chloro-S-hydroxytetracycline, is present as hydrochloride (melting point 212216 C., [04],; 22.5 (c.:1% in methanol containing 1% concentrated hydrochloric acid),

El? 400 at 266268 my and at 337-341 m;;).

The addition of isopropylether to the filtrate precipitates 1.1 gr. of 1la-chloro-6-deoxy-6-demethyl-6-methylene-5- hydroxytetracycline hydrochloride, showing a sole maximum in the 5-6/1. region at 5.72

3.3 grs. of the non-reacted lla-chloro derivative isolated above as hydrochloride is then treated with 10 mls. anhydrous hydrogen fluoride at a temperature of 5 C., during 3 hours. Afterwards, the hydrogen fluoride is distilled and the residue is dissolved in anhydrous methanol, the pH being adjusted to 5.5 with triethylamine. The 11achloro-6-deoxy 6 demethyl-6methylene-S-hydroxytetracycline base crystallizes slowly as solvate. The anhydrous base has the following characteristics: decomposition at 176 C., [a] +35 (c.=l% in methanol containing 1% concentrated hydrochloric acid),

13:? 371 at 270 my and 430 at 237-239 mg in methanol containing 1% hydrochloric acid; mgs. dissolve in 18 mls. of ethanol, 440 mls. of methanol, 22 mls. of dioxane, 60 mls. of acetone and 1 ml. of dimethylformamide. The infrared curve shows principal peaks at 2.8 4, 2.98 3.25 5.72 1, 6.08 6.3 1, 7.8a, 8.1 8.42,, 9.0a, 9.18,, 9.73 1, 10.6 10.76 L, 10.82/L, 11.6/L, 12.1, and 12.3

(e) 5 grs. of the non-reacted 11a-chloro-S-hydroxytetracycline hydrochloride, obtained according to (d), is suspended in 15 mls. of a mixture of 1:3 ethyl Cellosolve and butanol, followed by the addition of 15 mls. of hydrogen fluoride at 18 C. After stirring during 3 hours between 4 C. to 0 C., the hydrogen fluoride is eliminated through a nitrogen stream, and the product is precipitated by addition of isopropylether, yielding 4.4 grs. of 11a-chloro-6-deoxy-6-demethyl-6-methylene 5 hydroxytetracycline hydrofluoride, which decomposes at 220 C.,

421 at 235 my, 272 at 272274 III 4 and 60 3.13 377- 379 III 1.

in methanol. The infrared curve shows a sole maximum in the 56 region at 5.72 1.

Examples according to the present invention (1) 2.5 grs. of 10% palladium on charcoal and 2 mls. of diluted hydrazine hydrate 15% are added to 5 grs. of 11a-chloro-6-deoxy-6-demethyl 6 methylene-S-hydroxytetracycline hydrofluoride in 100 mls. of ethanol. 2.7 mls. of 15% hydrazine hydrate is added at the end of 15 minutes. After stirring overnight, the reaction mixture is filtered, and 5 grs. of S-sulfosalicyclic acid and 200 mls. of water are then added. After stirring during 1 hour, it is filtered, washed and dried. 5.5 grs. of 6-deoxy-6-demethyl-6methylene-S-hydroxytetracycline is thus obtained as 5 sulfosalicylate, and melts at 189-193 C., specific rotation [L]D 220 c.=1 in methanol containing 1% concentrated hydrochloric acid),

El'fi' 397 at 238 m and 219 at 345 m (2) 1.25 grs. of palladium on charcoal is suspended in 15 mls. of 70% aqueous dimethylformamide. 5 grs. of 1la-chloro-6-deoxy-6-demethyl 6 methylene-S-hydroxytetracycline-p-toluene-sulfonate dissolved in 25 mls. of 70% aqueous dimethylformamide and 2 grs. of hydrazine sulphate are then added. After stirring overnight. it is filtered, and 33 mls. of water and 5 grs. of 5-sulfosalicyclic acid are then added, yielding 4.9 grs. of methacycline sulfosalicylate, comparable with that obtained in Example 1.

(3) 2 mls. of 15% hydrazine hydrate is added to 5 grs. of 11a-chloro-6-deoxy 6 demethyl-6-methylene-5-hydroxytetracycline hydrofiuoride and 2.5 grs. of palladium on charcoal, followed by addition of further portions of 1 ml. of hydrazine hydrate at minute intervals, until the total amount of hydrazine hydrate 15%, reaches 8 mls. After stirring during 3 hours, 5 grs. of sulfosalicyclic acid and 200 mls. of water are added. After stirring for an additional hour, 3.6 grs. of methacycline sulfosalicylate are separated, containing about 8% of a-doxycycline demonstrated by paper chromatography (paper Schleicher Schiill No. 20436bgml-265 stationary solvent: Mc- Ilvain buiTer-pH 4.2, mobile phase: pyridine:benzene: nitromethane in a 3: 10:20 proportion).

The crude sulfosalicylate, thus obtained, shows a shoulder in its infrared curve at 10 indicating the presence of doxycycline. The optical rotation is [oc] '180 (c.=1 in methanol containing 1% concentrated hydrochloric acid), A 238 m 319 m 344350 ma. From the mother-liquors precipitated overnight a second crop weighing 1.6 grs. is obtained, which consists of a mixture of 60% methacycline and 30% doxycycline sulfosalicylate, according to paper chromatogram. The optical rotation of the crude product is [(11 ---160 (c.'=1 in methanol containing 1% concentrated hydrochloride acid),

Ew 409 at 238 my, 180 at 317 my, 194: at 340 my, 195 at 349 Ill 1..

(4) The procedure of Example 3 is repeated, but using platinum on charcoal instead of palladium. The crude sulfosalicylate, thus obtained, weights 3.8 grs. and contains approximately 41% methacycline, 53% a-6-de0xy-5-hydroxy-S-tetracycline and 4% fl-6-deoxy-5-hydroxytetracycline, according to the chromatographic assay.

I claim:

1. A process of dehalogenation and simultaneous dehalogenation and reduction of C6- of a lla-chloro-6-deoxy-6-demethy1-6-methylenetetracycline, wherein the 11achloro derivative is dehalogenated at C1 1aby equimolecular amounts of hydrazine to yield the respective 6-deoxy- 6-demethyl-6-methylenetetracyclines, and simultaneously dehalogenated at 11aand reduced at C6- by at least two equimolecular amounts of hydrazine to yield the respective 6-deoxytetracyclines, in the presence of catalytic amounts of a noble metal catalyst selected from the group consisting of palladium, platinum, and rhodium in an inert reaction medium, and the compounds thus formed are recovered subsequently from the reaction mixture.

2. A process according to claim 1, wherein the 11achlorotetracyclines are the lla-chloro derivatives of 6- deoxy 6 demethyl-6-methylenetetracycline, 6-deoxy-6- demethyl-6-methylene 5 hydroxytetracycline, 6-deoxy- 6-demethyl-6-rnethylene 7 chlorotetracycline and 6-deoxy-6-dernethyl-6-methylene 5 hydroxy-7-chlorotetracycline, in a form selected from free base and acid addition salts.

3. A process according to claim 1 wherein the reaction temperature is comprised between -10 to C.

4. A process according to claim 1, wherein the hydrazine is present as hydrochloride, sulphate or hydrate.

5. A process of preparation of 6-deoxytetracyc1ines containing predominantly the a-isomer, wherein the pH of the reaction mixture is maintained constant, between the value of 3 to 7, by the continuous slow addition of hydrazine.

References Cited UNITED STATES PATENTS 8/1965 Blackwood et al. 260559 AT OTHER REFERENCES DONALD G. DAUS, Primary Examiner A. M. T. TIGHE, Assistant Examiner 

1. A PROCESS OF DEHALOGENATION AND SIMULTANEOUS DEHALOGENATION AND REDUCTION OF C6- OF A 11A-CHLORO-6-DEOXY-6-DEMETHYL-6-METHYLENETETRACYLINE, WHEREIN THE 11ACHLORO DERICATIVE IS DEHALOGENATED AT C11A- BY EQUIMOLECULAR AMOUNTS OF HYDRAZINE TO YIELD THE RESPECTIVE 6-DEOXY6-DEMETHYL-6-METHYLENETETRACYCLINES, AND SIMULTANEOUSLY DEHALOGENATED AT 11A- AND REDUCED AT C6- BY AT LEAST TWO EQUIMOLECULAR AMOUNTS OF HYDRAZINE TO YIELD THE RESPECTIVE 6-DEOXYTETRACYCLINES, IN THE PRESENCE OF CATALYTIC AMOUNTS OF A NOBLE METAL CATALYST SELECTED FROM THE GROUP CONSISTING OF PALLADIUM, PLATINUM, AND RHODIUM IN AN INERT REACTION MEDIUM, AND THE COMPOUNDS THUS FORMED ARE RECOVERED SUBSEQUENTLY FROM THE REACTION MIXTURE. 